Housing for mounting HEPA filters

ABSTRACT

A housing for mounting HEPA filters includes an open-ended tubular casing (12) and, within said casing, slide structure (24) for slidably mounting a HEPA filter therein from one of the ends of the casing.  Baffle means (18) divides the interior of the casing into respective chambers (20, 22) which, on mounting of the filter in the slide structure (24), are gastight isolated from each other except by way of the filter and which are accessible from a respective one of the open ends of the casing. Also provided are gas intake/exhaust ports (46, 48) for each of the chambers (20, 22), a pair of cover members (14, 16) for closing the respective open-ends of the casing (12), each of which cover members (14, 16) includes a flange (94) complementary to the associated end of the casing (12), and respective clamp and seal means (100, 84) for clamping the cover members (14, 16) to the casing to effect gastight engagement of the flanges (94) with the respective ends of the casing (12).

This invention relates to a housing for the mounting of high efficiencyparticulate arresting (HEPA) filters used, inter alia, inmicrobiological isolation facilities. The filters typically form part ofair conditioning or ventilation systems used in heating, cooling orventilation of environments which are microbiologically contaminated orsterile.

HEPA filters are usually of multiple pleated construction. The natureand relationship of the pleats may vary but the filters are commonlycomparatively bulky and of generally box-like form. A long standingdifficulty has been to provide an installation for satisfactorilymounting HEPA filters in such a way that the installation will notnegate the rated performance of the filter (for example, an arrestanceefficiency of 99.97% or 99.99% when challenged with a mono dispersecloud of 0.3 micro meter Dioctyl Phthalate droplets) while on the onehand allowing easy access for installation of the filter and for leaktesting in situ, and on the other permitting acceptable gaseousdecontamination. This is measured by achieving a complete kill of aknown number of spores of the micro organism Bacillus subtilis varniger.

The present invention accordingly provides a housing for mounting HEPAfilters, comprising:

an open-ended tubular casing;

slide structure within said casing for slidably mounting a HEPA filterfrom one of the ends of the casing to a position intermediate said ends;

baffle means disposed to divide the interior of said casing intorespective chambers which, on mounting of the filter in said slidestructure are gastight isolated from each other except by way of thefilter and which are accessible from a respective one of the open endsof the casing;

gas intake/exhaust ports for each of said chambers;

a pair of cover members for closing the respective open-ends of thecasing, each of which cover members includes a flange complementary tothe associated end of the casing; and

respective clamp and seal means for clamping the cover members to saidcasing to effect gastight engagement of said flanges with the respectiveends of the casing.

The cover members are preferably of shallow convex configuration and maybe provided with a pair of spaced handles to facilitate theirapplication to and removal from the housing. Each clamp and seal meansmay comprise a band arranged to be clamped about the respective flangeand a sealing ring arranged to seat between the flange and theassociated end of the casing.

Said slide structure may comprise a set of guide rails secured to theinside surface of said casing so as to extend parallel to the centreaxis thereof. The rails may define four corner edge tracks for arectangular HEPA filter and are advantageously of lippedW-configuration. Such structure may be secured wholly within one of saidchambers and advantageously includes means for fastening the filter infirm engagement with said baffle means.

The tubular casing is advantageously of circular or ellipticalcross-section and may include a pair of co-axial but axially displacedtubular parts joined but separated by an annular extension of saidbaffle means.

The invention will be further described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of a HEPA filter housing constructedin accordance with the invention;

FIG. 2 is a partly exploded vertical axial cross-section through thehousing shown in FIG. 1, without the HEPA filter in place;

FIG. 3 is a less detailed view similar to that of FIG. 2 but showing thehousing installed in a building with the HEPA filter and associatedbutterfly isolating valves connected in place.

FIG. 4 is an end elevational view from the left in FIG. 1;

FIG. 5 is a cross-section on the line 5--5 in FIG. 1 with a filter inplace;

FIG. 6 is a cross-section on the line 6--6 in FIG. 2;

FIG. 7 is an enlargement of the region X of FIG. 2;

FIGS. 8 and 9 are enlargements of portions of FIGS. 2 and 5respectively, depicting portion of the filter slide structure, butshowing the filter in position;

FIG. 10 is an enlargement of the region Y of FIG. 2; and

FIG. 11 is a front detail view of part of a band clamp lever, showingits movement to the band open position.

The illustrated housing 10 includes an open-ended double-walled tubularcasing 12, respective cover members 14, 16 of shallow convexconfiguration for closing off the ends of casing 12, an internal baffle18 (FIG. 2) dividing the interior of casing 12 into separate chambers20, 22 and, wholly within chamber 20, slide structure 24 for slidablymounting a HEPA filter (11 in FIGS. 3, 8 and 9) within chamber 20 inabutment with baffle 18.

Casing 12 comprises an inner lining 26 of, say 1.6 mm, stainless steeland an outer cladding 28 of lighter gauge stainless steel, say 0.5 mm,encasing foamed polyethylene insulation 30. Lining 26 is actually in twoparts which are separated but joined by welding by an annular extension32 of baffle 18 (FIG. 7). This provision aids in ensuring a gastightconnection at the outer periphery of the baffle.

Baffle 18 is formed of four identical shaped plates 34, as best seen inFIG. 6. These plates are joined at gastight welds 36 to define a squarecentre opening 38 which registers with the HEPA filter on mounting ofthe latter in slide structure 24. At least the portions of plates 34which are engaged by the filter are surface treated for enhancedsmoothness, such as by surface grinding.

In situ, casing 12 is mounted atop a pedestal 40 (FIG. 3) which isfirmly secured on a concrete base 42 and carries a curved shoe 44 toseat casing 12. Gas flow through the interior of the casing is by way ofintake/exhaust ports 46, 48 which respectively communicate with chambers20, 22 and in use are fitted with gastight butterfly valves such asthose visible at 50, 51 in FIG. 3. Each port 46, 48 is defined by arespective flanged sleeve 52 which is welded about its inner peripheryto lining 26. Each sleeve 52 is penetrated (FIG. 5) by a seamlessstainless steel gassing pipe 54, also associated with a gastightbutterfly valve (not shown), to permit sterilization of the interior ofthe housing, and by a pressure tapping unit 56. All of the single portsmay be substituted by manifold arrangements if such are found to enhancereliability and/or performance.

Referring in particular to FIGS. 2, 5, 8 and 9, slide structure 24includes four uniform guide rails 60 which are secured to the innersurface of lining 26 symmetrically about axial planes at right angles toeach other and at 45° to the axes of sleeves 52. Each guide rail 60 issomewhat of the shape of a lipped "W" in cross-section, defining acentre right angle track 62 open towards the axis of housing 12, outerwebs 64, 65 also mutually at right angles, and edge lips 66 which abutand are welded to lining 26. The four right angle tracks 62 arepositioned to define a firm guideway for a HEPA filter of rectangularconfiguration, which guideway extends from just inside the outer end ofchamber 20 to a point displaced a short distance from baffle 18. Theouter end of rails may be flared to facilitate engagement of a filter inthe guideway.

The webs 64, 65 of each track 60 contain apertures 70 spaced along theirlength for selectively mounting a clamping frame to lock the filter inposition. This frame comprises four steel channels 72, each carrying apair of screw-threaded stubs 75 to which may be secured respective lugs74 (FIGS. 8 and 9) projecting from the rear rim of the filter. Theforward rim of the filter is typically provided with a neoprene gasket76 which engages baffle 18 about opening 36 and is clamped gastightthereagainst by fastening nuts 75a onto studs 75.

Studs 75 are of sufficient length to additionally mount a pre-filterassembly when such is considered desirable. When the housing is used inthe reverse mode, a pre-filter may be required in chamber 22 and to thisend baffle 18 carries a set of screw-threaded studs 77.

Attention will now be directed, with particular reference to FIG. 10, tothe arrangement by which each cover member 14, 16 is fastened in agastight manner to a respective open end of casing 12. At each end ofthe casing, lining 26 overlaps cladding 28, the tube being bridged by anannular plastics trim 27 glued to the lining at 27a and grooved to 27bto receive the end of the cladding. Lining 26 is pressed to form anannular outside bead 80 and an inwardly turned shallow lip 82. Bead 80is displaced rearwardly from lip 82 and defines a forward shoulder 81substantially at right angles to the axis of the casing. Shoulder 81received an elastomeric sealing ring 84 dimensioned to define an outsidediameter slightly less than that of bead 80.

Each cover member 14, 16 is, like casing 12, double lined, incorporatinga relatively thicker inner lining 86, a polyethylene insulation disc 87and an outer relatively thinner gauge cladding 88. Each cover member isslightly convex and carries a pair of symmetrically disposed handles 90fixed to cladding 88 above part-spherical recesses 92 (FIG. 4).

The outer peripheries of cover lining 86 are inturned and pressedtogether to define a flange 94 which is complementary to the end ofcasing lining 26. Flange 94 includes a first portion 96 which embracesthe extremity of lining 26 and an outwardly upset end portion 98dimensioned to fit snugly about and in contact with sealing ring 84. Thetwo components of flange 94 are fused together at the extremity of theflange.

At each end, lining 26, including shoulder 81, cover flange portion 98and sealing ring 84 are clamped together in a gastight manner by a bandclamp 100 which is of V-section and double lipped at 101 to embrace bead80 and cover flange portion 98. Each band clamp 100 is split and itsends are connected by an over-centre lock device 102, best seen in FIGS.4 and 11. Lock device 102 comprises a bifurcated arm 104 pinned to oneend of band clamp 100 and a lever 106 pinned at an extremity to theother end of the band clamp and at an intermediate point 105 to arm 104.Its action in altering the band clamp 100 from a band closed to a bandopen position, in which the band can be lifted away from the assembly topermit removal of the cover member, is best appreciated from aninspection of FIG. 11. In the closed position of the band, security sealmeans (not shown) is typically provided to prevent unauthorized removalof the cover member.

Cover lining 86 carries internal spring clips 108 which snap over casinglip 82 to locate the cover member as the band clamp is brought to itsclosed position. Lining 86 also mounts an annular array of externalclips 110 to seat the band clamp when the cover is disengaged from thecasing.

It is considered that the illustrated housing provides a highlysatisfactory solution to the problem of mounting HEPA filters inair-conditioning or ventilation systems. The tubular form of the housingassists in ensuring the required degree of gastightness. The form ofguide structure facilitates installation and removal of the fragilefilter elements. The filter itself if easily mounted into one of thechambers and brought to an operational position in which there is agastight seal between the two sides of the filter, apart from throughthe filter itself. The arrangement of the cover members permits easy andunobstructed access to the two chambers within the housing, and inparticular to the full upstream and downstream faces of the filter forthe purpose of leak testing in situ. The use of band clamps inassociation with the convex cover members ensures gastight closure andyet allows ready removal of the cover members.

I claim:
 1. A housing for mounting a HEPA filter in an air flow circuitof a building air-conditioning or ventilation system, including an openended tubular casing; baffle means formed to define an aperture anddisposed to divide the interior of said casing into respective chamberswhich are accessible from respective open ends of the casing; gas portsfor each of said chambers; and a pair of cover members for closing therespective open-ends of the casing, each of which cover members includesa flange complementary to the associated end of the casing;characterized by:slide structure within one of said chambers forslidably moving a HEPA filter to a position in said one chamber inengagement with said baffle means; first clamp means for clamping theforward end of the HEPA filter against said baffle means in a gastightengagement about said aperture by pressure applied to the rear end ofthe filgter; and second clamp means, independent of the first, andassociated seal means, for clamping the cover members to said casing toeffect gastight engagement of said flanges with the respective ends ofthe casing.
 2. A housing according to claim 1 further characterized inthat the casing is of circular or elliptical cross-section.
 3. A housingaccording to claim 1 or 2 further characterized by an outer tubular partco-axially embracing said axially displaced parts, the annular spacetherebetween being packed with solid matter.
 4. A housing according toclaim 1 or 2 further characterized in that said cover members are ofdouble walled construction.
 5. A housing according to claim 1 or 2further characterized in that said baffle means lies in a plane normalto the axis of the casing.
 6. A housing according to claim 1 or 2further characterized in that said casing and lower members are formedin sheet metal.
 7. A housing according to claim 1 or 2 furthercharacterized in that said first clamp means comprises multiple sets ofthreaded fixed studs and nuts engageable with lugs mounted to the rearend of the filter.
 8. A housing according to claim 1 or 2 furthercharacterized in that said casing and cover members are formed in sheetmetal.
 9. A housing according to claim 1 or 2 further characterized inthat the cover members are of shallow convex configuration.
 10. Ahousing according to claims 1 or 2 further characterized in that saidcover members are provided with two or more spaced handles to facilitatetheir application to and removal from the housing.
 11. A housingaccording to claim 1 or 2 further characterized in that the respectiveends of the casing include an external annular bead and in that saidflanges are flared to complement the respective beads.
 12. A housingaccording to claim 1 or 2 further characterized in that each secondclamp and seal means comprises a band arranged to be clamped about therespective flange and a sealing ring arranged to seat between the flangeand the associated end of the casing.
 13. A housing according to claim12 further characterized in that said band is of general V-section,bordered by narrow lips.
 14. A housing according to claim 1 or 2 furthercharacterized in that said slide structure comprises a set of guiderails secured to the inside surface of said casing so as to extendparallel to the centre axis thereof.
 15. A housing according to claim 14further characterized in that the rails define four corner edge tracksfor a rectangular HEPA filter.
 16. A housing according to claim 15further characterized in that the rails are of lipped "W" configuration.